This project studies the regulation of expression of genes encoding lens fiber membrane channel proteins, which are essential for maintaining the transparency and correct refractive index of the lens. We ar presently focusing on the regulation of expression of the gene encoding MIP, the major intrinsic protein of the lens fiber membrane, that is specifically expressed in the ocular lens fibers and belongs to an ancient family of transmembrane channel proteins. We have continued the study of the regulation of transcription of the MIP gene and have mapped several positive and negative cis regulatory elements in its 5'- flanking sequence. We mapped two negative regulatory regions in the human MIP 5'-flanking sequences-1564/-1696 and -948/-1000. We demonstrated that the human MIP 5'- flanking sequence -253/+42 contains a functional promoter in lens cells but is inactive in cultured nonlens cells, suggesting that this sequence contains regulatory elements responsible for the lens-specific expression of the MIP gene. We found that Sp1 and AP2 transcription factors interact with several domains of the human MIP gene promoter. The region -65/-37, containing an overlapping binding site for Sp1 and AP2, contains an important regulatory element for the activation of the MIP gene promoter in lens cells. We have cloned the mouse MIP gene and found that several regulatory domains are evolutionarily conserved. These studies will further our understanding of the regulation of the MIP gene expression in the lens.